A macro implementation of `strrchr()`

macro_strrchr.cpp

#include <iostream>
using namespace std;

#define _STRRCHR_IMPL_COMMON(str, ch, offset) (str)[sizeof((str)) - 1 - (offset)] == (ch)? (str) + sizeof((str)) - (offset): sizeof((str)) <= (offset) + 1? (str)

#define _STRRCHR_IMPL_31(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 31): (str))
#define _STRRCHR_IMPL_30(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 30): _STRRCHR_IMPL_31(str, ch))
#define _STRRCHR_IMPL_29(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 29): _STRRCHR_IMPL_30(str, ch))
#define _STRRCHR_IMPL_28(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 28): _STRRCHR_IMPL_29(str, ch))
#define _STRRCHR_IMPL_27(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 27): _STRRCHR_IMPL_28(str, ch))
#define _STRRCHR_IMPL_26(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 26): _STRRCHR_IMPL_27(str, ch))
#define _STRRCHR_IMPL_25(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 25): _STRRCHR_IMPL_26(str, ch))
#define _STRRCHR_IMPL_24(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 24): _STRRCHR_IMPL_25(str, ch))
#define _STRRCHR_IMPL_23(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 23): _STRRCHR_IMPL_24(str, ch))
#define _STRRCHR_IMPL_22(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 22): _STRRCHR_IMPL_23(str, ch))
#define _STRRCHR_IMPL_21(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 21): _STRRCHR_IMPL_22(str, ch))
#define _STRRCHR_IMPL_20(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 20): _STRRCHR_IMPL_21(str, ch))
#define _STRRCHR_IMPL_19(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 19): _STRRCHR_IMPL_20(str, ch))
#define _STRRCHR_IMPL_18(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 18): _STRRCHR_IMPL_19(str, ch))
#define _STRRCHR_IMPL_17(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 17): _STRRCHR_IMPL_18(str, ch))
#define _STRRCHR_IMPL_16(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 16): _STRRCHR_IMPL_17(str, ch))
#define _STRRCHR_IMPL_15(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 15): _STRRCHR_IMPL_16(str, ch))
#define _STRRCHR_IMPL_14(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 14): _STRRCHR_IMPL_15(str, ch))
#define _STRRCHR_IMPL_13(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 13): _STRRCHR_IMPL_14(str, ch))
#define _STRRCHR_IMPL_12(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 12): _STRRCHR_IMPL_13(str, ch))
#define _STRRCHR_IMPL_11(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 11): _STRRCHR_IMPL_12(str, ch))
#define _STRRCHR_IMPL_10(str, ch) (_STRRCHR_IMPL_COMMON(str, ch, 10): _STRRCHR_IMPL_11(str, ch))
#define _STRRCHR_IMPL_9(str, ch)  (_STRRCHR_IMPL_COMMON(str, ch, 9):  _STRRCHR_IMPL_10(str, ch))
#define _STRRCHR_IMPL_8(str, ch)  (_STRRCHR_IMPL_COMMON(str, ch, 8):  _STRRCHR_IMPL_9(str, ch))
#define _STRRCHR_IMPL_7(str, ch)  (_STRRCHR_IMPL_COMMON(str, ch, 7):  _STRRCHR_IMPL_8(str, ch))
#define _STRRCHR_IMPL_6(str, ch)  (_STRRCHR_IMPL_COMMON(str, ch, 6):  _STRRCHR_IMPL_7(str, ch))
#define _STRRCHR_IMPL_5(str, ch)  (_STRRCHR_IMPL_COMMON(str, ch, 5):  _STRRCHR_IMPL_6(str, ch))
#define _STRRCHR_IMPL_4(str, ch)  (_STRRCHR_IMPL_COMMON(str, ch, 4):  _STRRCHR_IMPL_5(str, ch))
#define _STRRCHR_IMPL_3(str, ch)  (_STRRCHR_IMPL_COMMON(str, ch, 3):  _STRRCHR_IMPL_4(str, ch))
#define _STRRCHR_IMPL_2(str, ch)  (_STRRCHR_IMPL_COMMON(str, ch, 2):  _STRRCHR_IMPL_3(str, ch))
#define _STRRCHR_IMPL_1(str, ch)  (_STRRCHR_IMPL_COMMON(str, ch, 1):  _STRRCHR_IMPL_2(str, ch))
#define _STRRCHR_IMPL_0(str, ch)  (_STRRCHR_IMPL_COMMON(str, ch, 0):  _STRRCHR_IMPL_1(str, ch))

// a macro version of strrchr().
// it has several limitations:
//   - str must be a literal string, e.g. "a string".
//   - if ch cannot be found in last 32 characters, it will return the whole string.
//     this limit can be increased by adding more _STRRCHR_IMPL_* macros.
#define _STRRCHR(str, ch) (sizeof((str)) <= 1? (str): _STRRCHR_IMPL_0(str, ch))

#define __FILENAME__ _STRRCHR(__FILE__, '/')

int main() {
	cout << "full file path: \t" << __FILE__ << endl;
	cout << "short filename: \t" << __FILENAME__ << endl;
	cout << endl;

	cout << "case 1: \n  expected: \tefgh.c\n  actual: \t" << _STRRCHR("0123/2345/4567/6789/8901/0123/2345/4567/6789/abcd/cdef/efgh.c", '/') << endl;
	cout << "case 2: \n  expected: \tabcdcdefefgh.c\n  actual: \t" << _STRRCHR("abcdcdefefgh.c", '/') << endl;
	cout << "case 3: \n  expected: \tabcd/cdef/0123456789012345678901234567890.c\n  actual: \t" << _STRRCHR("abcd/cdef/0123456789012345678901234567890.c", '/') << endl;
	return 0;
}

handle wchar_t[]

#define _STRRCHR_IMPL_COMMON(str, ch, offset)   (str)[sizeof((str)) / sizeof((str)[0]) - 1 - (offset)] == (ch) ?    \
                                             ((str) + sizeof((str)) / sizeof((str)[0])     - (offset)) :            \
                                                      sizeof((str)) / sizeof((str)[0])    <= (offset) + 1 ? (str)
...
#define _STRRCHR(str, ch) (sizeof((str)) <= sizeof((str)[0]) ? (str) : _STRRCHR_IMPL_0(str, ch))
#define __FILENAME__  _STRRCHR(__FILE__, '/')
#define __FILENAMEW__ _STRRCHR(__FILEW__, L'/')

fixed sizeof